17'3"
(5.3m) underwater protection consisting an outer void
compartment, two
liquid compartments, and an inner void compartment with a
holding
bulkhead. This was designed to withstand a 400 lb (181
kg) explosive charge.

Resembled the modernized Tennessee following
repairs from
1942-6 to 1944-1. However, light antiaircraft was 14x4
40mm guns, 40x2
20mm guns.

The Tennessees were
completed in 1920-1921. The Navy initially considered a radical
design
with armor sloped by as much as 45 degrees ("Ironsides"), but
abandoned this due to
stability concerns and chose a conventional design based closely
on the
New Mexicos.
They were
good ships, with turboelectric drive that improved subdivision.
They
were surprisingly
maneuverable, being able to reach full speed in just three minutes
and
with a
tactical diameter of 700 yards.

The most significant new feature of the ships was a
novel
underwater protection system, based on extensive caisson
experiments.
The system consisted of four compartments separated by thin
bulkheads.
The outermost and innermost compartments were void while the
middle
compartments were liquid-filled, and the bulkheads were designed
to
resist deformation as much as possible and then tear with as
little
fragmentation as possible. The effect was that most of the force
of a
torpedo explosion would be expended in the void spaces while the
liquid
layers absorbed fragments, leaving the inntermost holding bulkhead
intact to prevent flooding of the spaces beyond. The system was
judged
capable of resisting a 400 lb (181kg) explosive charge. It was the
best
engineered system in the world at the time, and its principles
were
duplicated on all subsequent U.S. battleships as well as many
foreign
battleships.

Another improvement was the use of turrets that could
elevate their guns to 30 degrees, which increased their range by
about
40% over earlier ship classes (which could only elevate their guns
to
15 degrees). This was judged valuable enough that the older ships
were
eventually modified to elevate their guns to 30 degrees as well.

Tennessee
was lightly
damaged in the Pearl
Harbor
attack, taking just two bomb
hits,
though her aft section was badly
damaged by
flaming oil from the Arizona. While under
repair, Tennessee added
considerable
antiaircraft armament and radar. Once new battleships began
arriving in
the Pacific, she was taken in hand for a major modernization that
left
her with a superstructure resembling South Dakota.

The two torpedoes that hit California
at Pearl Harbor failed to
penetrate her torpedo defense system. However, she had ten or
twelve
access hatches to her torpedo defense voids opened for inspection,
which allowed water to flood freely into the ship. She was later
raised and
repaired, undergoing her own extensive modernization, and
participated
in the final offensives of the war.